Sensors, for example gas sensors, are widely used and are known for many fields of use. For example, there are known gas sensors based on the principle of liquid electrochemistry or on the principle of thermal conduction. There are also known gas sensors which exploit MOS capacitors and capacity measurements, Schottky diodes and current/voltage measurements, field-effect transistors, heated semiconductive metal oxides and electrical resistance or conductivity measurements, or else ion-conducting membranes and potential measurements, as the detection principle.
The aforementioned gas sensors entail usually complex and hence costly production processes and therefore have a high cost, which means that they are only of limited usability for a multitude of applications and of restricted economic viability. Moreover, many of the aforementioned gas sensors have a not insignificant cross-sensitivity for constituents present in a gas other than those to be detected, for instance further gases, such that the measurement results obtained can have only limited accuracy. Furthermore, many gas sensors known from the prior art have an elevated working temperature, in some cases considerably elevated, compared to room temperature, which necessitates heating of the sensor for a measurement. As a result, sensors of this kind may under some circumstances be usable only to a limited degree, if at all, for portable applications. Moreover, as a result of high working temperatures, especially in the measurement of hydrogen, there is a risk of explosion, which should understandably be avoided. Furthermore, the need to heat a sensor always also leads to an elevated power consumption, which means that the sensor can only be of limited economic viability and, in addition, only of limited utility for portable applications. Moreover, the heating requires an additional heating layer or heating coil and electrical leads or electrical connections on the sensor.
DE 10 2006 020 253 B3 describes a titanium dioxide sensor for measurement of concentrations of reducing gases such as hydrogen, methane or ammonia. The sensor according to this publication consists of at least two layers of polycrystalline titanium dioxide on any desired substrate, which should withstand the final temperatures of approximately 500° C. for crystallization of the layers. The at least two layers of titanium dioxide are arranged one on top of the other, with the outer lamina, which forms the surface of the sensor toward the gas space, provided with catalyst particles present in the region of the particle interfaces, and the layer immediately beneath enriched with an alkali metal. A sensor of this kind should contain principally anatase titanium dioxide. The corresponding layers are produced by spin-coating or another sol-gel coating step.
A disadvantage of such a sensor is that, for a reliable and highly accurate measurement, it requires working temperatures within a range above room temperature, which is disadvantageous especially for a measurement of hydrogen and can also make the measurement inconvenient and costly. Furthermore, the production process for such a sensor is inconvenient and hence costly, which also makes such a sensor costly.